Bog pine dendrochronology related to peat stratigraphy: Palaeoenvironmental changes reflected in peatland deposits since the Late Glacial (case study of the Imszar raised bog, Northeastern Poland)

Abstract

Resultsof dendrochronological analysis of subfossil pine (Pinus sylvestris) buried in the Imszar raised bog deposits (NE Poland, Podlasie Region), were compared with multiproxy analysis of peat deposits (pollen and Non Pollen Palynomorphs, plant macrofossils, Cladocera, and geochemical analyses). The peat (3.3 m thick) accumulation started in the Allerød interstadial. The oldest pine tree population grew in this peatland in ca 6790–6530 cal yrs. BP: floating chronology (determined with the wiggle–matching method) covers this period is 255 years long. The growth of trees on the fen was related to the drying out of the fen at that time, which caused the break in peat accumulation (hiatus). Apart from numerous fallen trees excavated during the peat extraction, a horizon of vertical in situ tree trunks ingrown to the ground, were exposed during peat exploitation. On the basis of a dozen or so trees, a second, “dead forest” floating chronology 197 years long, was compiled with a time range of ca 4255-4060 cal yrs. BP. The youngest, third pine floating chronology (310 years long), elaborated on the basis of ex situ tree trunks, covers the time frame of ca 3130-2820 cal yrs. BP. Multiproxy analyzes of fen deposits indicate that the three stage colonization of the peatland by bog pine was associated with the periods of warming and overdrying in the climate of the Holocene, during which the groundwater table in the Imszar peatland significantly lowered. In turn, the dying off stages of the pine trees occurred in the phases of climate humidity growth, during which the groundwater level in the fen raised. They are well correlated with analogous bog pine germination and dying-off phases in the other European peatlands.